This document describes methods and devices that help prevent infections associated with the infusion or ingestion of fluids into the body.
An intravenous catheter is a hollow tube implanted through the skin for temporary or semi-permanent residence in a vein. It is used for infusion of various fluids including blood or blood products, for the withdrawal of blood, or to provide access to the circulation for other diagnostic or therapeutic purposes. Similar catheters may be inserted into arteries or other sterile internal structures for similar purposes. At times any of these catheters may be inserted across other internal body surfaces, including mucosa of the sinuses, oro-pharynx, gastrointestinal tract, genitourinary system, eye conjunctivae, etc. for similar or analogous purposes.
Most often these catheters are inserted into internal regions or structures that are sterile (i.e. devoid of infectious microorganisms). Because these catheters traverse the skin (or analogous body surfaces), they disrupt a crucial barrier preventing the entry of bacteria and other infectious microorganisms from the external environment into sterile regions inside the body. Indeed, such catheters are well known to represent a major source of infections in humans receiving medical care.
Two general mechanisms account for most infections caused by the insertion and continued presence of intravascular catheters, namely:                entry of infectious microorganisms through the skin opening around the exterior of the catheter, permitting them to colonize the catheter's exterior surface, and giving them direct access to subsurface tissues and deeper structures where they may cause infection; and        entry of infectious microorganisms, through opening in the fluid circuit connections and junctions, into the interior regions of the fluid circuit, including the lumen of the tubing and the inner surface of the catheter. These microorganisms contaminate the ostensibly sterile fluid, and are carried through the fluid circuit into the sterile interior of the body, causing infection in the blood stream or other structures at the downstream end of the catheter (so-called “intra-luminal infections”).        
The intravenous fluid circuit is the path of fluid flow from a syringe or fluid bag, through tubing, into the lumen of the intravenous catheter inserted into the body, and then into a blood vessel. This fluid path may include multiple tubing connections and ports. It is imperative that this intraluminal route remain sterile, to avoid introducing infectious pathogens into the circulation.
The catheter is sterilized before use, and routine catheter insertion into the patient utilizes procedures that are designed to maintain sterility. The tubing, ports and connectors upstream of the catheter connection in that fluid infusion circuit, as well as the solutions and medications infused through that circuit (“infusates”) are presterilized and connected so as to create and sustain a closed, sterile intraluminal environment throughout the circuit and catheter.
Conventional techniques have been developed to maintain that sterility every time the closed circuit is broken or entered for the infusion of additional fluids or medications, withdrawal of blood, or the attachment of additional circuits, ports, tubing, fluid bags, or devices. Nevertheless, every port and connection in the fluid circuit represents a potential site for the entry of infectious microorganisms.
Whenever a connection in the closed circuit is broken or a sealed port is removed, sterile interior surfaces of the circuit are exposed to the external environment. When so exposed, those sterile interior surfaces may become contaminated with infectious microorganisms, leading to intraluminal contamination and catheter colonization. Despite efforts to prevent these problems, utilizing optimized design of the fluid circuit components, and intensive education and training in preferred methods for sterile accessing of the fluid circuit, intraluminal contamination and infection remain a substantial problem in clinical medicine.
Once the fluid or the sterile internal surfaces of the catheter fluid path become contaminated with infectious microorganisms, it becomes extremely difficult to re-establish a sterile environment. Bacteria can become lodged within the interstices of the non-smooth surface micro-environment of commonly used medical plastics. Furthermore, and most critically, many bacteria secrete a biofilm during growth, which protects and covers the bacteria, rendering them virtually impervious to in situ mechanical, antiseptic and antibiotic eradication measures. In practical terms, once the fluid circuit becomes contaminated, it must be assumed that intraluminal surfaces of the fluid circuit may harbor adherent bacteria that cannot be removed.
Several approaches have been utilized to address actual or suspected catheter infections. The most direct is the removal of the catheter and its associated tubing and fluid bags, with the insertion of a new catheter, typically at another site.
An alternative but less effective method is the removal and replacement of all of the tubing and fluid path components upstream from the catheter, without removal of the catheter itself, in the (often vain) hope that although one or more of the circuit components may be colonized, the catheter itself has been spared.
Yet another approach is to insert a guide wire through the lumen of the catheter into the vein, remove the catheter over the guide wire, and then insert a new catheter over the guide wire into the same vessel location. This approach is sometimes successful. However, it is obvious that the guide wire can collect infectious microorganisms resident on the inner surface of the colonized tubing or catheter, and transfer them to the new catheter, thereby perpetuating rather than eliminating the unwanted colonization.
Antibiotics or antifungal medications have been infused through a contaminated catheter to kill the contaminating microorganisms. This approach has met with limited success most often because of the presence of microbial biofilm on the intraluminal surface of the catheter and other fluid circuit components. In principle, antiseptic solutions might also be used for decontamination of the inner surface of an intravenous catheter, but they are generally not suitable or safe for intravenous infusions at the concentrations needed for this decontamination process.
Another approach is the use of a filter inserted into the fluid path to block the passage of infectious microorganisms downstream of the filter, preventing catheter contamination and intravascular infection. Such filters do not block the passage of all infectious microorganisms, or all of their toxic products, and they do not address any contamination already present downstream of the filter.
U.S. Pat. No. 6,461,569 to Boudreaux discloses a device designed to eradicate infection on the internal surface of an indwelling intravascular catheter. The device utilizes an ultraviolet (UV) light source emitting microbicidal light in the UV-C spectrum. The light source is attached to a fiberoptic bundle that is inserted through the lumen of the intravenous fluid circuit and advanced to the site of presumed infection or bacterial colonization on the inner surface of an intravenous catheter. Irradiation of the bacteria with sufficient intensity and duration of UV light of appropriate wavelength can kill bacteria or render them incapable of proliferation. However, that device does not prevent the initial colonization of the catheter's inner surface, and does not block the infusion of infectious microorganisms into the patient. Furthermore, the use of this device breaks the closed fluid circuit, and therefore creates its own additional risk of microbial contamination of the fluid circuit.
Methods have been described to prevent colonization of the catheter with infectious microorganisms by depositing an antiseptic or antibiotic compound on the surface of the catheter, or within the structure or interstices of the catheter wall. These compounds may diffuse from the catheter wall into the adjacent infusate, blood or body fluid, where they exert their antimicrobial actions. In other arrangements, the compounds are chemically linked to the surface structure of the catheter, and directly interact with the infectious microorganisms in such a manner as to prevent adhesion, proliferation, or survival. Many different specific compounds and salts have been used; examples include silver salts, various antibiotics, and chlorhexidine. Clinical experience suggests that such specially treated catheters have modest but limited efficacy in preventing colonization by infectious microorganisms. The development of biofilm may render these compounds ineffective for their intended purpose.
In addition, problems exist with water supplies, as many supplies are located in remote locations that can become contaminated with microorganisms.
The presence of infectious microorganisms in the luminal fluid is likely to remain an inevitable consequence of the usage of intravascular catheters and similar devices for fluid infusion and blood withdrawal in contemporary medical practice. What is needed, therefore, is a device that will reduce or eliminate the risk that viable infectious microorganisms that may appear in the fluid circuit from being delivered downstream to contaminate the sterile catheter or cause infection of the systemic circulation. It is also desirable to provide a device that reduces or eliminates microorganisms from fluids that will be ingested into the body, such as water spigots or faucets.